1. Field of the Invention
This invention relates to a method of displaying, in real time, stream lins of an inhomogeneous flowing medium and a device therefor and, more particularly, to a device for displaying blood stream lines in a human heart in real time.
2. Description of the Related Art
In the art of medical electronics, an ultrasonic wave tomograph is used to display the conditions or motions of human organs on a cathode ray tube (CRT). Recently, Doppler tomography has been applied to the display of blood motion. This technique produces a flow map of blood as a two-dimensional tomogram using a color display. For example, a blood stream approaching a transducer, which generates and receives the ultrasonic pulse, is colored red and a stream travelling away from te transducer is colored blue, while the color tone is varied according to the speed of the blood stream. The speed of the blood stream is determined from a frequency shift, a phase shift or a distortion in the echo pulse caused by the Doppler effect associated with the moving blood. The process which obtains the speed of the moving body from the data is called a Doppler process, and hence, a tomograph using the process is called as a Doppler tomograph. The following U.S. Patents disclose the fundamentals of Doppler tomography intended for displaying blood flow: U.S. Pat. No. 4,182,173 to Papadeofrangakis et al, issued Jan. 8, 1980; U.S. Pat. No. 4,476,874 to Taenzer et al., issued Oct. 16, 1984; and U.S. Pat. No. 4,509,525 to Seo, issued Apr. 9, 1985.
In Doppler tomography, the measured speed of the blood flow is a relative speed of the blood in the scanning direction of the ultrasonic beam. The measured speed varies when the scanning direction is varied and, as a limit, the measured blood speed is zero when the blood stream is scanned orthogonally (perpendicular to blood flow direction). If the scanning direction is further rotated, the blood speed reverses.
An attempt to overcome the above problems has been proposed by K. Machii et al, in Proceedings of WFUMB '85, P. 382, in an article entitled "Clinical Usefulness of Power Mode Two Dimensional Doppler Colour Flow Mapping". The authors of the above paper detected a speed component of blood included in a Doppler tomogram obtained using a power echo of the ultrasonic beam. The application discovered is limited to a speed less than 0.1 m/s which is a very slow speed.
In addition, the prior art ultrasonic tomograph techniques cannot show blood stream lines. Essentially, blood stream lines are parallel to the blood vessel. In the past, the need to show blood stream lines has not been very high, however, recently, especially in the field of heart examination, it has become important to accumulate blood flow information on the heart. The heart is more like a chamber than a tube and it is not possible to anticipate the actual flow of blood from the appearance of the heart, especially of a ventricle. Accordingly, it has become important to display actual speed and direction, that is, blood stream lines in a tomogram. Until the present invention there has been no means available that can show the stream lines of blood flow in a human heart.